Dental implant treatment planning software systems normally work in two modes, single scan or dual scan. With single scan protocol, a patient is CT-scanned, the DICOM files are loaded into a software system, the jaw bone structure and remaining teeth are segmented and modeled in 3D space, and implant placements are simulated with the 3D bone/tooth model and the DICOM slices. In the dual scan mode, a so-called radiographic guide is made with radio-opaque markers. The patient is scanned wearing the radiographic guide, and the guide is then scanned separately. When the DICOM files are loaded into the system, the 3D bone/tooth model is created, the radiographic guide model is generated, and implants are placed with references to the 2D slices and the 3D model. More details of these workflows can be found in publications (Materialise, Philippe B Tardieu, etc.) and software documents of SimPlant, NobelGuide and EasyGuide, etc., which are the state-of-the-art of such workflows. All of the systems would place implants with 2D slices. SimPlant introduced 3D implant placement recently.
Very few publications are relevant to the topic that how implants are placed with references to CT scans data. Orentlicher (US 2007/0059665 A1) described a workflow in which CT scans are converted into files of some format, and doctors/technicians can download the converted files to place implants. Technically, this is same as what SimPlant has implemented. The converted files are the bone/tooth model and 2D slices, so the implant placement is based on the 2D slices and 3D bone/tooth model. Yang (US 2008/0193896) disclosed an approach trying to combine the CT scan data with physical cast models, which is related to the idea that implants need to be placed with references to the actual geometry of the patient's anatomy including soft tissues.
Another area of treatment planning system is the restoration preview. The idea is to put together a patient's anatomy structure, implants, abutments, and crowns to preview and evaluate the aesthetics of a treatment plan. The software function to add virtual teeth to the 3D graphics views can be found in commercial systems (www.materialise.com.Dental, SimPlant from Materialise). Unfortunately, the virtual teeth are added to a model with only jaw bones and teeth, other than a model that also includes soft tissues. This makes the virtual tooth functionality inconsistent with the actual needs of aesthetics evaluation.
As far as the soft tissue model is concerned, Christensen (U.S. Pat. No. 7,758,345B1) disclosed an approach to create a physical model with both bone and soft tissues from imaging data. A hard tissue model is created from scan data. So is a scan prosthesis (or radiographic guide in this disclosure) model. The hard tissue model is modified with some supporting structures, then the model of the scan prosthesis is attached to it, and finally “moldable” material is used to mold a model of the patient's soft tissue between the three-dimensional model of the scan prosthesis and the modified hard tissue model by pressing the three-dimensional model of the scan prosthesis against the one or more support structures.
From the implant placement to the restoration preview, surgical guide CAD/CAM, and implant surgery, there are three references involved. First is the implant placement reference. If the implants are placed with 2D DICOM slices, the slice data is the placement reference. If the 3D model combining jaw bones and teeth is used, in other words implants are placed in a 3D graphics view of the 3D model, this model would be the placement reference. The second reference is called “aesthetics reference” in the remainder of this document, which is basically a duplicate of the patients' anatomy including soft tissues. When the aesthetics of an implant case is assessed, one would like to see how the implants and restorations go along with the soft tissues. Using combinations of bone and teeth as aesthetics references is not a good practice, but has been the reality in prior art since the tissue models were not available. The third reference is the base model that is used to create a surgical guide. For a single scan case, the bone/tooth model will be trimmed and offset and drilled to create a surgical guide, so the surgical guide reference is the bone/tooth model. For dual scan cases, the model of the radiographic guide is registered with the bone structure, and then used as the base for the surgical guide.
With the state-of-art treatment planning, the placement reference may not be the surgical guide reference, and the aesthetics reference does not actually exist in treatment planning systems, which makes it impossible to preview restorations with the actual patient anatomy. The digital modeling of soft tissues, as well as its usage in planning stage, is missing in the implant planning systems and techniques.